MERCURY MOUNTAINEER ROOF PROBLEM

1998 Mercury Mountaineer

1998 Mercury Mountaineer 200000 miles

I have a leak in the top left corner of roof. Headliner gets wet and drips when raining. Took car to windshield repair garage and they found no leak. Thay said either the auto sunroof or the luggage rack is where leak is coming from. Thay said drain tubes from sunroof could be clogged. How do I check this and does this sound correct?